Exemplary embodiments of the present invention relate to a valve for one-time opening of a fluid line, in particular for venting a technical system. The invention further relates to a technical system, in particular of a spacecraft component.
Valves adapted for switching only a single time are frequently used in space travel. The function of the valves is to ensure a defined opening or closing of a fluid line at a given time. For this purpose, the valves have an actuator. In most cases, pyrotechnical igniters are used as actuators. A disadvantage of such actuators is that when actuating them, a so-called gyro-shock occurs, which can damage other components of the technical system. Pyrotechnical igniters normally have a limited warranted lifetime of, for example, 8 years. Since spacecrafts such as, for example, communication satellites typically stay longer than 15 years in geostationary orbit, a reliable actuation of the valve at the end of the lifetime of the system is not ensured.
Currently, one-time-switching valves on the basis of wax actuators are under development. In these actuators, a pre-loaded spring is embedded in wax. The solidified wax prevents the spring from relaxing. For actuating the valve, the wax is heated and thus liquefied. Due to the liquefied wax, the spring is no longer blocked and the actuator opens the cap of a capillary tube, for example by means of shear forces. The function of such an actuator requires the presence of a shear blade.
Exemplary embodiments of the present invention are directed to a valve that is to be opened only once and that allows in a cost-effective and reliable manner to open a fluid line, in particular for venting a technical system.
In accordance with the present invention the valve comprises an inlet for connecting to the fluid line, an outlet, and a controllable closure. The controllable closure is arranged between the inlet and the outlet and closes in the non-activated state a passage between the inlet and the outlet. The closure comprises a material that changes its phase state depending on a control parameter, as a result of which the passage is irreversibly opened in the activated state.
The valve according to the invention enables the one-time opening of a fluid line without a mechanical actuator. Through this, the valve can be produced with low complexity and therefore at low costs. Its reliable function is ensured over a lifetime of more than 15 years, as required in space applications.
The technical system can involve, for example, a space travel downthrust system with storable fuels. The proposed valve can be used, for example, to passivate satellite tanks and satellite lines, which serve for providing fuel and compressed gas, at the end of a mission. Through this, explosions can be prevented during a later re-entry of the spacecraft or in the event of debris impacts.
According to an advantageous configuration, the phase change of the material (so-called phase-change material) can be effected by heat supply, wherein the material transitions under heat supply from a solid state into a liquid state and thereby opens the closure. In order to achieve the phase change of the material, a so-called phase-change temperature has to be reached. The material is preferably selected such that the difference between an ambient temperature or an operating temperature of the valve and the phase-change temperature excludes unintentional actuation of the valve. Such unintentional actuation could be caused by solar radiation or waste heat of other components. Expediently, the phase-change material comprises a metal or consists of metal. Preferably, indium is used, which has a melting temperature of more than 157° C. and therefore meets the requirements placed upon space travel applications. The concept of metal is to be interpreted broadly. It is in particular to be understood that this also includes metal alloys.
According to a further advantageous configuration, the closure comprises a heating device that can be switched on by means of a control device so as to activate the closure. By means of the heating device, the material can be brought from the solid state, in which the closure closes a passage between the inlet and the outlet, into a liquid or gaseous aggregation state, whereby the one-time opening of the valve is enabled. The heating device can be configured as a resistance heating. A resistance heating system is known in fields related to space travel applications, for example, in connection with hydrazine jet engines. Such a heating device comprises a heating element, a feed line and an electrical connection.
Expediently, the heating device in the closure is arranged in spatial proximity to the phase-change material. This ensures that the reaction time for changing the phase state of the phase-change material is short.
In the non-activated state of the valve, the phase-change material closes at least one passage channel of the closure. In other words, this means that the closure has one or a plurality of passage channels in which, in the non-activated state, the solid phase-change material is arranged. After activating the valve, the fluid contained in the fluid lines flows through the passage channel or channels for venting the technical system.
According to an advantageous configuration, a wall of the at least one passage channel, in a longitudinal section through the closure or through the evacuation valve, is formed to be conical or stepped at least in sections so that the material is pressed against the wall by the pressure prevailing in the technical system. This ensures that the pressure prevailing during the operation of the technical system cannot displace the sealing phase-change material when the evacuation valve is not activated, which otherwise could result in leakages of the technical system.
In a further configuration, the outlet has an outlet nozzle that has at least one opening, wherein the outlet nozzle protrudes into a volume of the valve, which volume is arranged between the passage and the outlet, wherein the material that is liquefied by activation can be absorbed by the volume, and the at least one opening of the outlet nozzle is fluidically connected to the inlet by passing through the passage. Here, the at least one opening is connected to an exit of the outlet. The volume formed in the housing of the valve thus is dimensioned in terms of its size in such a manner that the material that changes its phase state during heating can be completely absorbed by said volume. At the same time, the outlet nozzle is arranged in the volume in such a manner that the at least one opening of the outlet nozzle is not closed by the phase-change material, and the connection between the inlet of the evacuation valve and the outlet of the evacuation valve is therefore ensured.
The outlet can be formed such that it has at its exit a tube for connecting. Alternatively, the outlet can comprise a nozzle at its exit. The nozzle can be connected here as a separate component to the outlet of the evacuation valve. Likewise, the outlet of the evacuation valve can be configured such that the exit of the outlet has the shape of a nozzle. In a further variant, the outlet can comprise at its exit a plurality of outlets which enables the fluid to discharge symmetrically, in particular along a longitudinal axis of the evacuation valve. This ensures that during discharging of the fluid, no thrust vector or no moment is generated that acts on the technical system, for example, a satellite or a spacecraft. Such an arrangement is also designated as “zero-force-outlet”.
For limiting the fluid flow rate when the valve is open, an orifice can be arranged between the inlet and the closure. This orifice limits the cross-section through which the fluid can flow during venting of the technical system. Corresponding to this, alternatively or additionally, an orifice for limiting the fluid flow rate can also be arranged between the outlet and the closure.
When reference to a fluid is made in the present description, this is to be understood as both a liquid medium and a gaseous medium, for example, a fuel.
The technical system involves in particular a spacecraft component that comprises an evacuation valve that is configured as described above. Here, as long as the valve is not open, the medium in the technical component is typically pressurized.